The - in this case, Senior Member of the - Tribunal steps into the original decision-maker's shoes. The original decision-maker (and therefore the Tribunal) was bound by the Civil Aviation legislation. From the decision at the link:
By section 9A of the Act, CASA and therefore this Tribunal, is required to regard the safety of air navigation as the most important consideration in the exercise of its powers under the Act.
The remarkable thing to me is that such a 'dangerous' pilot was able to survive for 20 + years before the discovery by CASA of his 'dangerous' levels of pain-killing medication.
It must be that the same level of medication in Australia has a more deleterious effect on pilots in Australia than in the USA, and even moreso if CASA finds out about it.
Remarkable.